1. Field of the Invention
The present invention relates to a method of and an apparatus for adjusting the tension of a timing belt chiefly used for an engine for vehicles.
2. Description of the Prior Art
Hitherto, a method has been publicly known, as disclosed in Kokai (Laid-Open) publication No. 60-164607 of Japanese Patent Application for adjusting the tension of a timing belt in an engine. The engine has an engine body, a crankshaft, a driving pulley on the crankshaft, a driven pulley on a camshaft of a valve operating mechanism, an auxiliary pulley for a water pump unit, an oil pump unit, etc., a timing belt bridged over these pulleys, and a tension pulley for pressing a loose side portion of the timing belt from outside. The tension pulley is pressed to be advanced while a predetermined torque is being applied to the driving pulley in its normal rotation direction at the same time that the driven pulley is fixedly held. The tension pulley is then fixed at the advanced position thereof.
The auxiliary pulley is generally disposed between the driven pulley and the driving pulley on the loose side of the timing belt. Since the auxiliary pulley has internal frictional resistance, a partial looseness of the timing belt between the auxiliary pulley and the driven pulley cannot be completely removed simply by such pressing and advancing the tension pulley as carried out by the foregoing conventional method. Even if the predetermined torque is applied to the driving pulley, a tension force acting on the tension side portion of the timing belt is not constant due to ununiform varied frictional forces of the crankshaft. Consequently, the tension of the timing belt cannot be accurately adjusted to obtain a desired tensioned condition.